Wireless communications have shifted from bit rates of few Mbps to Gbps in order to accommodate the increasing demand of bandwidth during the last ten years. Such increase in data rates has been achieved by means of using higher modulations schemes, improved channel codes, MIMO transmissions, etc. Nevertheless, the use of larger parts of the overall spectrum remains still the most effective and simple way to increase the network throughput.
In the case of cellular networks, operators have started to use the unlicensed band as a means of decongesting the scarce and expensive licensed spectrum. For instance, 3GPP Rel. 12 allows mobile devices to do offloading using an IEEE 802.11 network.
Coexistence with 802.11 WLANs has already been studied for Bluetooth, Zigbee and WiMaX. In the non-patent literature of Eduardo Almeida et al., “Enabling LTE/WiFi coexistence by LTE blank subframe allocation”, in Communications (ICC), 2013 IEEE International Conference on, pages 5083-5088, a coexistence mechanism is proposed between LTE and 802.11 WLANs based on Almost Blank Subframes (ABS), i.e., almost silent periods in LTE transmissions, which is later extensively evaluated with simulations in the non-patent literature of Andre M Cavalcante et al., “Performance evaluation of LTE and Wi-Fi coexistence in unlicensed bands”, in Vehicular Technology Conference (VTC Spring), 2013 IEEE 77th, pages 1-6, and analytically in the non-patent literature of Alireza Babaei et al., “On the impact of LTE-U on Wi-Fi performance, “in Personal, Indoor, and Mobile Radio Communication (PIMRC), 2014 IEEE 25th Annual International Symposium on, pages 1621-1625.
In the non-patent literature of Cristina Cano and Douglas J Leith, “Coexistence of WiFi and LTE in unlicensed bands: A proportional fair allocation scheme”, in Communication Workshop (ICCW), 2015 IEEE International Conference on, vol., no., pp. 2288-2293, 8-12 Jun. 2015, and in the non-patent literature of Ahmed K Sadek et al., “Extending LTE to unlicensed band-merit and coexistence”, in Communication Workshop (ICCW), 2015 IEEE International Conference on, pages 2344-2349, coexistence mechanisms and methods are proposed giving a certain degree of fairness.
All the aforementioned methods show that the throughput of LTE can be improved, but none of them are compliant with Listen-Before-Talk, ‘LBT’ mechanisms as specified in the non-patent literature of ETSI, EN 301 893 v1.8.1: “Broadband Radio Access Networks (BRAN); 5 GHz high performance RLAN; Harmonized EN covering essential requirements of article 3.2 of the R&TTE Directive”. Therefore, they can only be deployed in some regions.
In the non-patent literature of 3rd Generation Partnership Project, 3GPP TR 36.889 v13.0.0—“Study on licensed-assisted access to unlicensed spectrum (release 13)” a range of LBT-compliant mechanisms and respective evaluations are presented. The results show that in some scenarios LTE-U can be configured to not degrade an 802.11 station more than if another station were added to the network. Nevertheless, the conventional configurations are implementation-dependent and some of the parameters are unlikely to be known in real networks. Further, none of the conventional methods determines how much additional throughput an LTE-U can obtain.
A further conventional method is Carrier Sense Adaptive Transmissions, ‘CSAT’, which comprises adapting the time a channel is used by an LTE station in order to provide coexistence/fairness to the network. CSAT however does not have any control on the access mechanism to the channel, i.e., it does not take into account if the channel is being used by a WiFi station.
In the US Patent Application US2015/0023315, a base station, ‘BS’, is disclosed a) performing a Clear Channel Assessment, ‘CCA’, and then b) transmitting a first waveform to a set of UEs over unlicensed spectrum when channel is sensed as idle. This is used for channel reservation. Then, one or more user equipment UE reply back with another waveform to indicate nearby WiFi devices that a BS has channel access, and another waveform to provide the BS with information for data transmission.
Other conventional methods are disclosed in the United States Patent Application US2015/0049741 and in the United States Patent Application US2015/0049712 for downlink and uplink unlicensed access respectively. In the United States Patent Application US2013/0343288 a power control for LTE is proposed to operate in unlicensed bands with minimum impact to WiFi networks while maximizing channel utilization. A conventional LBT scheme is disclosed in the United States Patent Application 20140362780 for carrier aggregation in the uplink using CCA.